1. Field of the Invention
The present invention relates to a cooling structure for a battery pack constituted by arranging a plurality of prismatic battery modules parallel with each other.
2. Description of Related Art
A conventional cooling structure for a battery pack, in which a plurality of prismatic battery modules are arranged parallel with each other, is disclosed, for example, in Laid-open Japanese Patent Application No. 3-291867. With reference to FIG. 4 which illustrates the battery pack 21 according to this publication, a plurality of battery modules 22 are arranged such that their side faces of largest area face each other. The cooling medium passages 23 are formed between these battery modules 22, 22. In the illustrated example, the cooling medium passages 23 comprise horizontal grooves 24 formed over the entire length at the bottom of the cases of battery modules 22 and a plurality of spaced vertical grooves 25 extending from these horizontal grooves 24 and reaching the upper face of the case. Reference numerals 26 and 27 represent a positive terminal and a negative terminal, respectively, and reference numeral 28 represents connecting terminals whereby battery modules 22, 22 are electrically connected in series. Reference numeral 29 denotes safety vents.
In this conventional cooling structure of a battery pack, cooling medium passages 23 are formed between the battery modules 22 by providing grooves in mutually opposed side faces of the cases of battery modules 22, or, by providing mutually abutting projections such as circular protrusions or linear ribs. The battery modules 22 are cooled by means of convection currents in these cooling medium passages 23 or by forcibly passing cooling medium therethrough.
However, with such construction as shown in FIG. 4, if the area of cooling medium passages 23 is increased in the widthwise direction in order to enhance the battery cooling efficiency, the wall thickness of battery modules 22 is decreased accordingly, as a result of which sufficient wall surface strength in regard to the internal pressure of the battery cases cannot be ensured. On the other hand, if the wall thickness of the cases of the battery modules 22 is made large in order to ensure the wall strength, the cooling efficiency becomes poor, because the heat within the battery modules cannot be effectively transmitted to their outer surfaces.
In view of the foregoing, it is an object of the present invention to provide an improved cooling structure for a battery pack.
In a cooling structure according to the invention for a battery pack wherein prismatic battery modules are arranged parallel with each other in a condition such that their side faces of largest area face each other, cooling passages are formed by interposing spacers made of metallic material between the mutually opposed side faces of the battery modules.
With this battery pack cooling structure, since the spacers are made of metallic material, they can be made large for supporting the side faces of the battery modules over a wide area without compromising the heat transfer effect. Since the side walls of the battery cases are supported over a large area by the spacers, the wall thickness of the battery cases can be reduced, whereby the heat transfer effect can be enhanced. Reduction in the wall thickness in turn increases the cooling medium passage area. Thus the cooling structure of the present invention exhibits excellent cooling performance.
Preferably, the spacers are made of a sheet bent in opposite directions such that alternately protruding grooves respectively contact the opposite long side faces of the battery modules. Heat within the battery modules is thereby transferred into the cooling medium directly or through the contacting spacers having a high heat transfer coefficient, and dissipated swiftly. The pitch space between adjacent protruding grooves of the spacers is set relatively small, so that the side faces of the battery cases are supported over a wide area with sufficient strength. In this way, the wall thickness of the side faces of the battery cases can be made small, while maintaining sufficient support for the battery cases. Furthermore, the width of the cooling medium passages can be made large to the extent that the wall thickness is reduced, whereby the cooling efficiency is remarkably enhanced.
The spacers can be made of corrugated sheet having a wavy cross-section, or of extrusion moldings or pultrusion moldings formed with grooves or cavities constituting the cooling medium passages.
The spacers are preferably made of aluminum or aluminum alloy, because it exhibits high heat transfer performance and has other advantageous properties such as light weight and good ductility. Any other materials that have similar properties can of course be employed.
While novel features of the invention are set forth in the preceding, the invention, both as to organization and content, can be further understood and appreciated, along with other objects and features thereof, from the following detailed description and examples when taken in conjunction with the attached drawings.